The primary objective of this study is to determine the extent which amino acids are absorbed during one exchange of Nutrineal in order to evaluate daily losses of proteins & amino acids into dialysate. The secondary objective is to evaluate if there is an association between peritoneal membrane transport characteristics and amino acid uptake from Nutrineal. Stable continuous ambulatory peritoneal dialysis (CAPD) patients will undertake their dialysis as usual, with one Nutrineal exchange on day three.